I. Field of the Invention
The present invention relates generally automatic apparatus for inverting workpieces for subsequent milling. More particularly, the present invention relates to a system for inverting workpieces entering a milling machine, and for reinverting them after machining. Known prior art is classified in U.S. Patent Class 414, Subclasses 762, 763, 766, 769 and 773.
II. Description of the Prior Art
Modern computer controlled milling machines are capable of a variety of machining operations. Typical milling machines comprise a machine head with a rotating spindle shaft that handles a plurality of machine tools, including chip removal tools, rotary tools, milling cutters and the like. Usually a carousel adjacent to the milling head stores the desired tools for computer selection and transfers them to the milling head as manufacturing progresses. As machining progresses, chips and dross are dislodged from the area of chip formation in response to cutting fluid spraying and gravity. Milling debris such as metallic chips and particles collect at the bottom of the usually enclosed machining volume, and are removed through chip extraction systems known in the rt. Obviously as a result of gravity the dislodged chips and debris, which may be spun off in a variety of directions during machining, ultimately move downwardly to the machine bottom. It is a known advantage to have chips drop downwardly, as they may get out of the way of subsequent machining operations. However, depending upon the orientation of the workpiece and the relative position of the milling head, not all chips and debris drop directly downwardly.
If dislodged milling debris does not quickly evacuate the region of the workpiece being machined, its presence can cause a number of problems.
As the chips get in the way of the machine tool, the workpiece may become deformed, cutting tools become dull more quickly, and manufacturing tolerances may not be met. Particularly bad cases can result in tool breakage, and the marring of the workpiece finish. If the chips are removed quickly and efficiently, better manufacturing precision and speed is achieved. Machine tool life can be extended as well.
To maximize the cleansing effect of gravity upon dislodged chips or debris, the point of machining (i.e., where the machine tool cutter engages the workpiece) must be established below the rest of the structure, near the lowest point of the workpiece within the machining volume. The amount of necessary machining near the bottom of the workpiece depends upon a variety of factors, including the type and duration of the required machining operation, the size and configuration of the workpiece, and the type of materials involved. It has been recognized that advantages can be obtained when milling certain workpieces in an inverted orientation. However, it would seem desirable to provide an inverting system that may be retrofitted to existing milling equipment so that all workpieces to be machined may be placed in the most desirable orientation.
Conventional reversing apparatus use vacuum suction cups that grip a workpiece in one horizontal position and then rotate the workpiece 180 degrees. According to this reversal system, the vacuum suction cups must be lifted high and retracted to be outside the area of rotation. An example of this design can be found in U.S. Pat. No. 4,498,840. One problem associated with systems of this type is when raising the cups high requires the use of a tall reversing apparatus and a long and complex piping system connected to the suction cups. Another problem is that suction cups may not adequately grip workpieces with irregular surfaces. Yet another problem is the reversal procedure is a prolonged and hence, inefficient operation.
Another design for inverting a workpiece can be found in U.S. Pat. No. 4,715,775. It is proposed here to invert large-scale heavy material such as a metal mold through a combination of gears. This process requires the use of complicated gear mechanisms, clutches and motors. U.S. Pat. No. 2,862,629 discloses an inverting mechanism that utilizes a plurality of worm wheels for inverting large numbers of paper sheets. Another gear driven transfer mechanism is disclosed in U.S. Pat. No. 4,056,198. A reversible drive oscillates in unison a pair of gearboxes through 180 degrees. The gearboxes carry shafts with arms of equal length mounted thereon. Grippers attached to the ends of the arms attach to the lateral edge of the work piece. One problem found in systems of this type is that they cannot be fitted to an existing system. Also, the complex gear and drive systems increase the need for maintenance and thus increase the cost of operation.
Designs for rotating a package 180 degrees have been proposed, an example of which may be found in U.S. Pat. No. 5,141,388. A gripper element is movably mounted to a linear carriage. The gripper element on the basis of a control signal can grip and release a package. Through the use of a slotted guide and a control cam the package is rotated as it moves along a work area. In U.S. Pat. No. 4,573,863 it is proposed to use a set of clamp arms disposed about a conveyor to grip a package. When actuated, die clamp arms are elevated and rotated 180 degrees after which the clamp arms are lowered back to the conveyor in an inverted position. U.S. Pat. No. 4,523,670 and Euro. Pat. No. 0 233 657 discloses method of transferring and orienting a workpiece that utilize clamps and conveyors. One problem with designs of this type they only allow for the simple raising and lowering of a workpiece on a conveyor belt or the like. Another problem is they are not adaptable to existing machines.